Cosmetic sunscreen products have the object, chiefly owing to the content of suitable UV filters, of protecting the skin from sunburn. However, the efficiency of the protection is inversely proportional to the tanning which is achieved, that is to say the greater the protection the less the tanning of the skin.
It remains the desire of every sunbather to achieve, after the shortest possible exposure to the sun, the optimal, dark, long-lasting and natural tanning of the skin.
The present invention has the object of providing a cosmetic sunscreen product which, in addition to the customary protection from radiation by UV filters, and the skin-care properties of the product base, allows, on exposure to the sun, more rapid, darker, more persistent and biologically natural tanning of the skin than do known products of this type.
Extensive research into skin pigmentation has shown that rapid, dark and persistent tanning of the skin depends not on the number of pigment-forming cells but on the efficiency of the metabolic processes in the pigment cells of the skin.
It is known that the skin pigment melanin is produced in the skin from tyrosine, an amino acid. This conversion of tyrosine takes place by an oxidative bioreaction under the influence of light, heat and oxygen. This reaction, that is to say the transfer of oxygen to tyrosine, is made possible in the skin by an enzyme, tyrosinase.
Based on this known biological process, it was obvious to add to sunscreen products tyrosine, the starting substance for the formation of melanin, in the hope that, by this means, there would be more intense tanning on sunbathing. This has now been attempted, but it emerged that it was possible to achieve only a slight intensification of tanning by this addition. It is not possible to add the enzyme tyrosinase, which occurs in the skin, as activator to the tyrosine-containing sunscreen products now known, because the enzyme is difficult and costly to obtain and is chemically unstable. The intrinsic coloration exhibited by other activators now used is unfavorable.